Switched-mode power supplies (SMPS) are commonly used and increasingly replacing “classical” power supplies composed of a transformer and a linear voltage regulator. SMPS use switching power converters to convert one voltage (e.g., an AC line voltage or a 13.8 V battery voltage) into another voltage, which may be used as supply voltage for an electric device or an electronic circuit. Many different switching power converter topologies are known in the field, such as buck converters, boost converters, Ĉuk converters, flyback converters, etc.
For safety reasons, it is desirable for the output of the power converter circuit to include galvanic isolation from the input circuit (connected to the utility power grid). The isolation averts possible current draw from the input source in the event of a short circuit on the output and may be a design requirement in many applications. Usually, optocouplers are used to galvanically isolate a feedback signal representing the regulated output voltage from the input circuit of the power converter circuit. The power conversion is accomplished by using a transformer. Transmitting feedback signals via optocouplers to ensure galvanic isolation often entails a comparably complicated feedback circuit.
Another design goal for the power conversion from the incoming AC line power to the regulated DC output current may be accomplished through a single conversion step controlled by one switching power semiconductor. A one-step conversion maximizes circuit efficiency, reduces cost, and raises overall reliability. Switching power conversion in the circuit design is necessary but not sufficient to satisfy the one-step conversion requirement while capitalizing on the inherent efficiency.
There is a need for a SMPS circuit that provides a regulated output voltage while not requiring any feedback signals to be tapped at the voltage output. Thus, optocouplers or similar components, which are usually employed for transmitting the current feedback signal back to the input circuit while providing a galvanic isolation, can be disposed of.